audio_device: Update explicit feedback support

Feedback can be specified by the user code and will be
sent at feedback endpoint specified interval.

src/class/audio/audio_device.c

@@ -121,10 +121,9 @@ typedef struct
 #if CFG_TUD_AUDIO_EPSIZE_OUT
   CFG_TUSB_MEM_ALIGN uint8_t epout_buf[CFG_TUD_AUDIO_EPSIZE_OUT];        // Bigger makes no sense for isochronous EP's (but technically possible here)
 
-  // TODO: required?
-  //#if CFG_TUD_AUDIO_ENABLE_FEEDBACK_EP
-  //    uint16_t fb_val;                                                 // Feedback value for asynchronous mode!
-  //#endif
+#if CFG_TUD_AUDIO_ENABLE_FEEDBACK_EP
+  uint32_t fb_val;                                                       // Feedback value for asynchronous mode (in 16.16 format).
+#endif
 
 #endif
 
@@ -643,18 +642,51 @@ static bool audiod_tx_done_type_I_pcm_ff_cb(uint8_t rhport, audiod_interface_t*
 // This function is called once a transmit of an feedback packet was successfully completed. Here, we get the next feedback value to be sent
 
 #if CFG_TUD_AUDIO_EPSIZE_OUT && CFG_TUD_AUDIO_ENABLE_FEEDBACK_EP
-static uint16_t audio_fb_done_cb(uint8_t rhport, audiod_interface_t* audio)
+static bool audio_fb_send(uint8_t rhport, audiod_interface_t *audio)
 {
-  (void) rhport;
-  (void) audio;
+  uint8_t fb[4];
+  uint16_t len;
 
-  // Here we need to return the feedback value
-#error RETURN YOUR FEEDBACK VALUE HERE!
+  if (audio->fb_val == 0)
+  {
+    len = 0;
+    return true;
+  }
+  else
+  {
+    len = 4;
+    // Here we need to return the feedback value
+    if (rhport == 0)
+    {
+      // For FS format is 10.14
+      fb[0] = (audio->fb_val >> 2) & 0xFF;
+      fb[1] = (audio->fb_val >> 10) & 0xFF;
+      fb[2] = (audio->fb_val >> 18) & 0xFF;
+      // 4th byte is needed to work correctly with MS Windows
+      fb[3] = 0;
+    }
+    else
+    {
+      // For HS format is 16.16
+      fb[0] = (audio->fb_val >> 0) & 0xFF;
+      fb[1] = (audio->fb_val >> 8) & 0xFF;
+      fb[2] = (audio->fb_val >> 16) & 0xFF;
+      fb[3] = (audio->fb_val >> 24) & 0xFF;
+    }
+    return usbd_edpt_xfer(rhport, audio->ep_fb, fb, len);
+  }
 
-  if (tud_audio_fb_done_cb) TU_VERIFY(tud_audio_fb_done_cb(rhport));
-  return 0;
 }
 
+//static uint16_t audio_fb_done_cb(uint8_t rhport, audiod_interface_t* audio)
+//{
+//  (void) rhport;
+//  (void) audio;
+//
+//  if (tud_audio_fb_done_cb) TU_VERIFY(tud_audio_fb_done_cb(rhport));
+//  return 0;
+//}
+
 #endif
 
 // This function is called once a transmit of an interrupt control packet was successfully completed. Here, we get the remaining bytes to send
@@ -918,7 +950,7 @@ static bool audiod_set_interface(uint8_t rhport, tusb_control_request_t const *
           }
 
 #if CFG_TUD_AUDIO_ENABLE_FEEDBACK_EP
-          if (tu_edpt_dir(ep_addr) == TUSB_DIR_IN && ((tusb_desc_endpoint_t const *) p_desc)->bmAttributes.usage == 0x10)   // Check if usage is implicit data feedback
+          if (tu_edpt_dir(ep_addr) == TUSB_DIR_IN && ((tusb_desc_endpoint_t const *) p_desc)->bmAttributes.usage == 1)   // Check if usage is explicit data feedback
           {
             _audiod_itf[idxDriver].ep_fb = ep_addr;
 
@@ -1215,13 +1247,9 @@ bool audiod_xfer_cb(uint8_t rhport, uint8_t ep_addr, xfer_result_t result, uint3
     // Transmission of feedback EP finished
     if (_audiod_itf[idxDriver].ep_fb == ep_addr)
     {
-      if (!audio_fb_done_cb(rhport, &_audiod_itf[idxDriver]))
-      {
-        // Load with ZLP
-        return usbd_edpt_xfer(rhport, ep_addr, NULL, 0);
-      }
+      if (tud_audio_fb_done_cb) TU_VERIFY(tud_audio_fb_done_cb(rhport));
 
-      return true;
+      return audio_fb_send(rhport, &_audiod_itf[idxDriver]);
     }
 #endif
 #endif
@@ -1403,4 +1431,16 @@ static bool audiod_verify_ep_exists(uint8_t ep, uint8_t *idxDriver)
   return false;
 }
 
+#if CFG_TUD_AUDIO_ENABLE_FEEDBACK_EP
+bool tud_audio_fb_set(uint8_t rhport, uint32_t feedback)
+{
+  audiod_interface_t *audio = &_audiod_itf[0];
+
+  audio->fb_val = feedback;
+  TU_VERIFY(!usbd_edpt_busy(rhport, audio->ep_fb), true);
+
+  return audio_fb_send(rhport, audio);
+}
+#endif
+
 #endif //TUSB_OPT_DEVICE_ENABLED && CFG_TUD_AUDIO

src/class/audio/audio_device.h

@@ -259,6 +259,11 @@ TU_ATTR_WEAK bool tud_audio_rx_done_cb(uint8_t rhport, uint8_t * buffer, uint16_
 
 #if CFG_TUD_AUDIO_EPSIZE_OUT > 0 && CFG_TUD_AUDIO_ENABLE_FEEDBACK_EP
 TU_ATTR_WEAK bool tud_audio_fb_done_cb(uint8_t rhport);
+// User code should call this function with feedback value in 16.16 format for FS and HS.
+// Value will be corrected for FS to 10.14 format automatically.
+// (see Universal Serial Bus Specification Revision 2.0 5.12.4.2).
+// Feedback value will be sent at FB endpoint interval till it's changed.
+bool tud_audio_fb_set(uint8_t rhport, uint32_t feedback);
 #endif
 
 #if CFG_TUD_AUDIO_INT_CTR_EPSIZE_IN

src/device/usbd.h

@@ -377,6 +377,11 @@ TU_ATTR_WEAK bool tud_vendor_control_complete_cb(uint8_t rhport, tusb_control_re
 #define TUD_AUDIO_DESC_CS_AS_ISO_EP(_attr, _ctrl, _lockdelayunit, _lockdelay) \
 		TUD_AUDIO_DESC_CS_AS_ISO_EP_LEN, TUSB_DESC_CS_ENDPOINT, AUDIO_CS_EP_SUBTYPE_GENERAL, _attr, _ctrl, _lockdelayunit, U16_TO_U8S_LE(_lockdelay)
 
+/* Standard AS Isochronous Feedback Endpoint Descriptor(4.10.2.1) */
+#define TUD_AUDIO_DESC_STD_AS_ISO_FB_EP_LEN 7
+#define TUD_AUDIO_DESC_STD_AS_ISO_FB_EP(_ep, _interval) \
+		TUD_AUDIO_DESC_STD_AS_ISO_FB_EP_LEN, TUSB_DESC_ENDPOINT, _ep, (TUSB_XFER_ISOCHRONOUS | TUSB_ISO_EP_ATT_NO_SYNC | TUSB_ISO_EP_ATT_EXPLICIT_FB), U16_TO_U8S_LE(4), _interval
+
 // AUDIO simple descriptor (UAC2) for 1 microphone input
 // - 1 Input Terminal, 1 Feature Unit (Mute and Volume Control), 1 Output Terminal, 1 Clock Source